1. Field of the Invention
This invention relates to an intra-aortic balloon catheter system.
2. Description of the Related Art
The intra-aortic balloon pump (IABP) is a temporary circulatory assist device for patients with extreme low cardiac output syndrome, e.g. after myocardial ischemia due to coronary heart disease. IABP catheters for aortic counterpulsation have been described in several previous patents (U.S. Pat. Nos. 4,733,652; 5,484,385; 5,697,906; 5,711,754; 5,759,175).
This device, based on the principle of counterpulsation, improves the blood supply of the heart muscle and other organs during cardiogenic shock or open heart surgery for coronary bypass grafting and subsequently decreases the mortality of these patients.
Usually, the IABP catheter is placed in the femoral artery using the guide wire technique: after puncturing the vessel, the guide wire is introduced. This wire is needed to install a percutaneous introducing sheath, i.e. an arterial line with larger inner diameter than the outer diameter of the IABP catheter. At the proximal end, this sheath has an hemostatic valve, which is used for a non traumatic introduction of the IABP catheter, e.g. in the femoral artery.
Distally, a long narrow balloon is attached to the catheter body that is connected to a computer controlled pump system via the proximal end of the catheter. Depending on the clinical requirements the ECG or the femoral pulse triggers the inflation and deflation of the catheter balloon with helium or carbon dioxide gas. The inflation occurs at the end of the systolic phase of the heart beat, i.e. right after closure of the aortic valve, and produces an increased intra-aortic pressure, followed by elevated coronary and systemic blood flow. Exactly before the next systole is about to start, the balloon is deflated to avoid an extensive afterload to the already damaged heart.
The medical indication of the IABP system is life threatening insufficiency of the heart and the circulation. As a consequence, these patients require intensive cardiovascular monitoring to guarantee optimal therapy strategy. One of the most important parameters in this context is the actual performance of the heart, the cardiac output (CO) or cardiac index, respectively.
Determination of CO is routinely performed by pulmonary thermodilution with a right heart catheter (RHC) orxe2x80x94alternativelyxe2x80x94by transpulmonary arterial thermodilution: with this technique, no RHC for hemodynamic monitoring is necessary. An arterial line with integrated thermistor is inserted percutanousely into the femoral artery with Seldinger technique and connected to a corresponding CO monitor. Via a conventional central venous line a defined amount of normal saline, e.g. 10 ml, with a defined temperature significantly below the blood temperature, at least room temperature, Is injected rapidly. The CO catheter in the femoral artery records changes in the blood temperature caused by the indicator following the same principle as the RHC. Depending on myocardial function, washout of the indicator Is accomplished fast or slow. According to the theory of Stewart and Hamilton, the CO can be calculated by the integral of the indicator dilution curve:   CO  =                    V        i            ·              (                              T            B                    -                      T                          i              ⁢                              xe2x80x83                                                    )            ·      K                      ∫        0        ∞            ⁢              Δ        ⁢                  xe2x80x83                ⁢                  T          B                ⁢                  xe2x80x83                ⁢                  ⅆ          t                    
where: xcex94TB is the blood temperature change after injection,
Vi is the injectate volume,
TB is the blood temperature before injection,
Ti is the injectate temperature,
K is a correction factor taking into account specific heat and weight of injectate and blood and loss of indicator during injection.
Assessment of cardiac output simultaneously to IABP is usually performed by introducing a RHC.
U.S. Pat. No. 3,995,623 discloses a multipurpose flow directed catheter (right heart catheter). This catheter is flow-directed through the heart of the patient by a balloon on its distal end to pass through the right atrium, right ventricle and into the pulmonary artery. A thermistor proximal to the balloon permits monitoring of blood temperature and thus allows the determination of cardiac output by the thermodilution technique.
Measurement of CO with a RHC however means increased strain and risk for further complications for the critically inpatient. Several studies in the last few years have demonstrated significant incidence of complications in association with the use of the RHC, especially infections and traumatic lesions, or even increased mortality due to the device itself.
Determination of CO by transpulmonary thermodilution in the femoral artery simultaneously to the treatment with the IABP is not advisable. The contralateral femoral artery not used for IABP has to be cannulated for the placement of the CO catheter. Catheters would occupy both femoral arteries and in case of an emergency operation this may be problematic, since the available femoral artery normally is the emergency access for extracorporeal circulation.
It is therefore an object of the present invention to overcome the deficiencies of the prior art devices by providing an IABP enabling an online measurement of the cardiac output without an additional intravascular access and without interruption of the circulatory assist of the IABP.
A further object of the present invention is to provide a IABP catheter which allows the determination of cardiac output without using a right heart catheter (Swan-Ganz-catheter).
A still further object of the present invention is to provide an IABP catheter which allows the determination of the cardiac output with minimal stress and risk for the critically ill patient.
In accomplishing these and other objectives of the present invention, there Is provided an intra-aortic balloon catheter system comprising a temperature sensor (thermistor). Such a thermistor is comparable with thermistors used in RHC or arterial thermodilution catheters and is suitable for the determination of CO.
Placement of the thermistor in the catheter may vary, however, the tip of the thermistor is constantly in the blood stream to ensure an optimal recording of the change in blood temperature. One possible position for the thermistor is on the outside of the catheter body about 2 cm behind the tip (distal end). In this case it has to be ensured that the thermistor tip is not covered respectively isolated by the material of the catheter body. In this way a heating of the surrounding material and subsequently an indicator loss for the thermistor is avoided. The typical response time of the thermistor is comparable to those in RHCs or arterial thermodilution catheters.
The course of the thermistor wire would preferably be in the inner lumen of the body of the catheter.
Alternatively, the thermistor can be introduced separately after placement of the IABP catheter via the port of the inner lumen: for this possibility, the thermistor wire is equipped-with markings or delineations providing information about the depth of the thermistor location within the patient: for optimal measurements the thermistor tip has to overtop the IABP catheter tip about 1 to 2 cm for a proper placement in the free blood stream.
All different technical units of the system are divided in different channels at the proximal end of the catheter: one for the gas pump, one for the arterial blood pressure measurement and the thermistor line with a transpulmonary thermodilution computer. Subsequently, the catheter can be connected to every clinically used commercial monitoring system as long as it is equipped with the necessary algorithm for calculation of transpulmonary cardiac output and derived variables.
Other features, characteristics and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings.